Moe, V., & Aune, T. K. (2009). The effect of stretching on muscle force production in hamstring muscles. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

This study explored the acute effect of proprioceptive neuromuscular facilitation (PNF) stretching on maximal voluntary contraction, rate of force development, and power in both isometric and dynamic contractions of the hamstring muscles (knee flexion) in male kickboxers (N = 10). Ss were tested randomly with or without stretching over two days. The day without PNF served as a control condition. Each experimental condition included a 10-minute warm-up on at treadmill at 60% of the Ss' HRmax. Immediately after warm-up on the day without stretching, the dependent variables in both the isometric and dynamic contractions of the hamstrings were tested. After warm-up on the stretching day, Ss underwent a controlled PNF sequence of the hamstrings that was followed immediately by a test of the dependent variables. Ss' hamstring flexibility was controlled by the "sit and reach test" after warm-up both days of testing, and after the PNF experience. Only the dominant leg was tested.

Proprioceptive neuromuscular facilitation increased hamstring flexibility, but negatively affected maximal voluntary contraction, rate of force development, and power in both isometric and dynamic contractions of the hamstring muscles.

Implication. PNF has an acute negative effect on muscle force production in both isometric and dynamic tasks. It might not be the type of stretching to be employed before performing activities that require high force production.

[This is the first study reviewed by this editor that has reported negative findings associated with PNF stretching. There are a number of considerations that need to be heeded when contemplating this investigation. From this editor's perspective, and that of the Coaching Science Abstracts, there is only one form of PNF stretching that is worthwhile. It was originally promoted by Lawrence E. Holt, Ph.D. as "3S Stretching" in his now out-of-date book, (Holt, L. E. (1973). Scientific Stretching for Sport. Halifax, Nova Scotia: Dalhousie University). Recently, the 3S technique was re-introduced by Humana Press of New Jersey (Holt, L. E., Pelham, T. W., & Holt, J. (2008). Flexibility: A Concise Guide to Conditioning, Performance Enhancement, Injury Prevention and Rehabilitation).

When evaluating stretching research, and in particular PNF stretching, it is helpful to consider the following factors:

What was the method used?

What controlled PNF sequence was used?

What were the tests used and the delay of time between exercise and testing?

How were the tests related to the stretching technique, that is, were the tests truly valid? [For example, in the study reported here, it is not clear when one and two legs were involved in stretching and/or testing.]

Was there a follow-up with a second test after a delay period to measure the duration of the effect?

Despite the various forms of PNF stretching that have developed deliberately or by a failure to adhere to the original protocol standard, there still is an overwhelming body of evidence that supports PNF stretching as being the only safe and beneficial form of deliberate stretching work. When it is combined with free-form "safe" ballistic stretching (now commonly referred to as "dynamic stretching"), its use in performance preparation is beneficial and advisable. BSR]